INVESTIGATION ON THREE LEVEL ISOLATED PFC CONVERTER

Abstract

For low-cost isolated ac/dc power converters adopting high-voltage dc-link, research efforts focus on single-stage multilevel topologies. This project proposes a new single-stage three-level isolated ac/dc PFC converter for high dc-link voltage low-power applications, achieved through an effective
integration of ac/dc and dc/dc stages, where all of the switches are shared between two operations. With the proposed converter and switching scheme, input current shaping and output voltage regulation can be achieved simultaneously without introducing additional switches or switching actions. In addition, the middle two switches are turned on under zero current in discontinuous conduction mode operation, and the upper and bottom switches are turned on under zero voltage. Due to the flexible dc-link voltage structure, high power factor can be achieved at high line voltage. A500 W/48Vprototype is designed to serve as the proof of concept, which exhibits 90.8% peak efficiency at low input line voltage. With this proposed converter, the input current shaping and output voltage regulation can be achieved with the help of microcontroller based soft switching technique and it does not require any additional switches. Through this soft switching technique, the inverter switches are turned on under zero current and zero voltage in discontinuous conduction mode operation. Due to the flexible dc-link voltage, high power factor can be achieved with regulated dc output. A 300W/110V prototype is designed and developed for the proof of concept, which shows the power factor is in the range of 0.96 to 0.99.